1. Field of the Invention
The present invention relates to a hydraulic accumulator capable of accumulating an operating liquid under pressure (i.e., capable of accumulating a pressurized operating liquid) in a liquid chamber formed within a shell serving as a pressure vessel. More specifically, the present invention relates to a metal bellows hydraulic accumulator in which a bellows unit for dividing the interior of the shell into a gas chamber and a liquid chamber has a bellows portion formed of metal.
2. Description of the Related Art
A metal bellows hydraulic accumulator of such a type is disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 2002-155901. In the disclosed metal bellows hydraulic accumulator, a bellows unit having a bellows portion formed of metal is disposed within a pressure space formed in a pressure vessel, whereby the pressure space is sectioned into a gas chamber filled with a predetermined pressurized gas, and a liquid chamber communicating with a liquid passage formed in the pressure vessel. The liquid chamber is further sectioned into a first liquid chamber to which the bellows portion of the bellows unit is exposed, and a second liquid chamber to which the liquid passage is opened. Further, an open-close valve is provided between the first and second liquid chambers. When the open-close valve is opened, the first and second liquid chambers communicate with each other. When the open-close valve is closed, the first and second liquid chambers are brought out of mutual communication, whereby the amount of contraction of the bellows portion of the bellows unit is restricted.
In the above-described conventional metal bellows hydraulic accumulator, so long as the open-close valve functions properly, the amount of contraction of the bellows portion of the bellows unit is restricted upon closure of the open-close valve, whereby the bellows unit is protected. However, when the open-close valve becomes unable to properly function because of breakage of a constituent member thereof, protection of the bellows unit is not expected, and debris produced as a result of breakage of the constituent member is mixed into operating liquid as foreign matter. Such foreign matter flows out of the accumulator together with the operating liquid, and may adversely affect a hydraulic circuit including the accumulator.